(1) Field of the Invention
The present invention relates to a sheet post-processing device for subjecting printed sheets to stapling and the like, for use in an image forming apparatus, and more detailedly, relates to a post-processing device which can contribute to miniaturization of an image forming apparatus.
(2) Description of the Prior Art
Conventionally, there have been image forming apparatus which have a post-processing means such as a stapler etc., for subjecting the sheets to post processes. With concern to the post-processing means, various technologies have been disclosed.
For example, Japanese Patent Application Laid-Open Sho 64 No.34868 and Japanese Patent Application Laid-Open Hei 1 No.209270 disclose sheet post-processing devices in which a post-processing means is arranged under a post-processing tray for holding sheets to be post-processed.
This sheet post-processing device is constructed so that the sheets placed on the post-processing tray are post-processed at their corners by a post-processing means disposed under the post-processing tray and then the thus post-processed sheets are discharged from the post-processing tray. This arrangement makes it unnecessary for the post-processing means to remove when the sheets are discharged. Further, discharge of the sheets after post-processing from the post-processing tray can be realized with a fixed sheet guide means which is provided close to the post-processing tray.
Japanese Patent Application Laid-Open Hei 8 No.310717 and Japanese Patent Application Laid-Open Hei 10 No.324445 disclose sheet post-processing devices capable of effecting post-processes at the center of each side of the sheets, in addition to their corners only.
The sheet post-processing device disclosed in Japanese Patent Application Laid-Open Hei 8 No.310717 is so constructed that the post-processing means can move along the discharged direction of the sheets already discharged, effect the post-process on the side perpendicular to the discharged direction of the sheets already discharged and retracts in the direction perpendicular to the discharged direction of the already discharged sheets so as to allow for pickup of the sheets after the post-processing treatment. Here, since this post-processing device is configured so as to effect its post-processing task over the sheets having been discharged on the discharge tray, the discharge tray functions as the post-processing tray.
In the post-processing device disclosed in Japanese Patent Application Laid-Open Hei 10 No.324445 the post-processing means is arranged on the side of the post-processing tray opposite to the direction in which the sheets after post-processing are discharged, and post-processing is effected on the sheet edge opposing the post-processing means, and the sheets after post-processing are discharged by a pusher.
However, in the sheet post-processing device disclosed in Japanese Patent Application Laid-Open Hei 8 No.310717, the post-processing means is constructed so as to approach, and retract from, the sheets placed on the post-processing tray, in the direction perpendicular to the discharged direction of the sheets. Therefore, when a post-process is implemented at the middle of the first discharged sheet edge, the distance between the position on the sheets at which the post-process is effected and the sheet edge perpendicular to that from which the sheets are discharged becomes large, hence the arm of the post-processing device needs to be long, which proportionally makes the post-processing means greater.
For post-processes such as stapling sheets with a stapler or punching on sheets using a punch, a relatively large drive force is needed. This is all the more so, i.e., a greater drive force becomes needed when the arm of the post-processing device becomes longer. This results in the problem that the post-processing device becomes complicated and large due to the increase in size of the drive source such as a motor, due to the necessity of a multiple reduction gear configuration and the like.
In such a post-processing means, the above problem becomes more distinct if the direction in which the post-processing means advances to and retracts from the sheets corresponds to the length of the sheets.
In the sheet post-processing device disclosed in Japanese Patent Application Laid-Open Hei 8 No.310717, in order to inhibit the increase in size of the post-processing means to as little as possible, the device configuration is devised so as not to enlarge the distance between the position on the sheets at which the post-process is effected and the sheet edge perpendicular to that from which the sheets are discharged, by adopting a long-edge feed scheme if the entry direction of the sheets relative to the post-processing tray and the direction of sheet discharge from the post-processing tray are the same.
However, this configuration poses a new problem that the advantage obtained when the sheets are fed in their short-edge direction, or the reduction in sheet feed time and reduction in job completion time cannot be obtained.
For the sheet post-processing device disclosed in Japanese Patent Application Laid-Open Hei 10 No.324445, it is possible to solve the problems with the sheet post-processing device disclosed in Japanese Patent Application Laid-Open Hei 8 No.310717, explicitly, the bulky configuration of the post-processing means, complexity of the drive mechanism of the post-processing means, the large drive source of the post-processing means and the like.
Nevertheless, since the space used upon the movement of the post-processing means, the space for the input means to carry sheets into the post-processing tray and the space for the discharging means to discharge the sheets from the post-processing tray, need to be secured individually, this inefficiently consumes the space inside the post-processing device, resulting in obstruction against design flexibility and leading to the bulkiness of the machine.
This situation is the same as in the case of the sheet post-processing device disclosed in Japanese Patent Application Laid-Open Hei 8 No.310717.
The present invention has been proposed under the circumstances described above, and it is therefore and object of the present invention to inhibit an increase in size of the arm portion of a post-processing means, increase in size of the drive source of the post-processing means, complexity of the drive mechanism of the post-processing means and the like even if the post-processing means which is disposed on the side from which the post-processed sheets are discharged to the discharge tray is constructed so as to advance to or retract from the sheets in order to effect a post-process over the sheets or discharge the sheets. It is another object of the present invention to prevent increase in size of the device attributed to the necessity of individually securing within the device, the space used for the movement of the post-processing means, the space for the conveying means to convey sheets into the post-processing tray and the space for the discharging means to discharge the sheets from the post-processing tray.
In order to achieve the above object, the present invention is configured as follows:
In accordance with the first aspect of the present invention, a sheet post-processing device includes:
a post-processing table for stacking sheets;
a post-processing means capable of moving between the post-processing position where a post-process is effected on the sheets stacked on the post-processing table and the retracted position where the post-processing means is retracted from the sheets placed on the post-processing table so that the sheets can be discharged;
a conveying means which conveys sheets into, or discharging sheets from, the post-processing table, and has a part which retracts from the space occupied by the post-processing means when the post-processing means is moved to the post-processing position and which also occupies the same space when the post-processing means is moved to the retracted position; and
a shifting means for moving the post-processing means and the conveying means part in such a manner that the conveying means part retracts from the space occupied by the post-processing means when the post-processing means is moved to the post-processing position and moves and also moves into the space occupied by the post-processing means when the post-processing means moves back to the retracted position.
In accordance with the second aspect of the present invention, the sheet post-processing device having the above first feature further includes: a stopper means which moves between a blocking position where discharge of the post-processed sheets on the post-processing table is blocked and the free position where discharge of the post-processed sheets on the post-processing table is permitted, wherein only after the post-processing means has moved to the retracted position and the conveying means part has also moved to the space occupied by the post-processing means, the stopper means moves from the blocking position to the free position.
In accordance with the third aspect of the present invention, the sheet post-processing device having the above first feature is characterized in that the post-processing means rotates about an axis extending in a direction perpendicular to the discharged direction of sheets in the post-processing table so as to be retracted to the side opposite to the sheet stacking face of the post-processing table.